Radiation treatment is very effective for the treatment of squamous cell and basal cell skin cancers for human patients. Historically, superficial 250 KV external beam radiation provided a good tool for such treatment with excellent control and cosmetic results. However, such equipment is no longer available, and is bulky, expensive, and requires highly skilled operators.
Currently, superficial radiation treatment with electron beams is provided for treating certain skin cancers through a long course of multiple therapy sessions (fractional therapy) which may require daily therapy for several weeks and the depth of the radiation dose for such therapy is usually several centimeters. Such a fractional course is long, expensive, and inconvenient to patients. In addition, cosmetic results from electron beam radiation therapy to the skin are often compromised due to irradiation of subcutaneous tissue underlying the desired treatment site which does not need to be targeted therapeutically.
In brachytherapy procedures, catheters or guide tubes are used which are, in some procedures a guide tube is used which is positioned externally at a desired orientation relative to a patient's skin area to be treated. A radioisotope source is loaded into the guide tube and is moved robotically inside the guide tube to topically expose tissue surrounding the source to a desired radiation dose and is thereafter withdrawn. This is referred to as high dose rate or HDR brachytherapy. This procedure is distinguished from low dose rate or LDR brachytherapy in which a radioisotope source is implanted for exposure over a long period (months or years) or implanted permanently. The radiation exposure dose of brachytherapy is intended to cause radiotoxicity and destroy targeted human tissue, for example cancerous skin cells.
In HDR brachytherapy for treating skin cancer, an applicator component is used which forms a fixture for supporting and orienting a brachytherapy guide tube and further for shielding radiation exposure along ray paths not providing desired exposure of the skin area to be treated. A brachytherapy treatment machine is used to accurately position the radioisotopes source in the guide tube during a treatment session. Typically the position of the radioisotope source is moved within the guide tube after stopping at dwell positions. A control wire inside a flexible brachytherapy guide tube is attached to the guide tube which is in turn mounted to the applicator. The brachytherapy treatment machine moves the radioisotope source to desired dwell positions on a time schedule within the applicator by moving the control wire.
Single channel brachytherapy applicators for treating skin cancers are known. These devices employed a single guide tube for the radioisotope source. The use of single channel brachytherapy applicators results in uneven radiation distribution to skin surface and superficial depth, resulting in a very high dose in the center area of the applicator as compared to peripheral regions in the treatment field area. Due to limitations of such devices, treatment of skin cancer has been limited due to lack of good applicators with standardized radiation distribution limited to several millimeters in depth. Another known system utilizes a single channel source oriented in a vertical orientation, which is also not conducive to uniform dose distribution pattern; this results in a very uneven dose distribution, relative low dose at center of applicator surrounded by a high dose zone then a very low dose at periphery of treatment area.